Studies will be carried out on the basic mechanisms of electrical excitation in nerve cell membranes. In particular, a further investigation of a new quantitative description of the sodium conductance, in terms of a coupled activation - inactivation process will be conducted. The aim of the investigations will be to: (1) expand the range of experimental phenomena which can be accounted for by this model (but not by Hodgkin - Huxley kinetics), (2) decide which alternative physical interpretations of the model are consistent with the quantitative values extracted. In addition the selectivity of the sodium channel in Myxicola giant axons to various alkali cations will be examined using internal perfusion. Such data on selectivity sequences are essential for the construction of models for the ion translocation process.